Live data showing high MAF and Absolute throttle Position

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New Member
Feb 8, 2011
clk320, sl320
Hi everyone. Decided to purchase a very cheap high mileage E220 convertible ( I know what youre all thinking !).
It had a recon'd engine fitted by a local garage but they never got it running properly as the customer didnt want to spend any more on it. Ive got to the position of having it running and driving Ok ish.
Just started playing with the new scanner (topdon artidiag 800 bt) and on Live data at idle ive got MAF showing 25g/s and Absolute Throttle position as 86.667%, both being well out of expected range and showing RED to make it easier for us simple people. Accelerator peddle shows 4.7% on both sensors. The car idles quite well though ! ECU software must be very clever !
I have changed the Throttle valve to be on the safe side. However it shows 86.667 % even when not running, Maf shows 0g/s as expected. My thinking is the throttle butterfly surely cant be fully open or it wouldnt idle, and as it drives OK too. The high MAF reading does however indicate that the engine is gulping huge amounts of air at idle. I have swapped for a known good MAF too.
Am i correct in thinking that the throttle valve is two parts. The butterfly which is controled by the accellerator position and the sensor that 'sees' the movement then feeds back to the ECU ?
Otherwise, how would it drive ?
Ive discovered an 'Intake port shutoff actuator' on a wiring diagram. What does that do ? I have discovered that it shares +5v with the throttle valve from a connector in the harness by the look of it.
I am hoping to get a meter on the connections over the weekend weather depending. Does anyone know what the feed back from the throttle valve signal should be at idle ? will I need a scope to check properly ?
As you can guess Im not shure where to go from here. The car sometimes throws an MIL with MAP sensor on the inlet manifold, but given the problems Im not surprised.
Does anybody have any ideas ? and a logical approach on testing procedures ? I can back probe the connector on the Throttle Valve to check + and ground reference voltages but I cant find anything on the Signal values. Im not very good with WIS either !!
Thanks to anyone that can throw any light on this. I thought my 129 was complicated electronically, but the engine is simple to understand !
Thanks to anyone who reads this.


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